In recent years, the drainage pipe industry has developed new types of flexible corrugated drainage and irrigation tubing wherein the wall thereof includes alternating annular peaks and valleys and a plurality of peripheral slotted openings arranged transversely to the longitudinal axis of the tube. The Sixt U.S. Pat. No. 3,699,684 discloses in Col. 3 lines 7-11 that such drainage tubes can be coiled on a drum such as its shipping container and simply fed down into a trench immediately after it is dug. A sheet of flexible water-repellent material may be placed over the area of the tube in which the slotted openings are located. Alternatively a sheet of fine filtering material may be used instead of the water-repellent material.
Such a combination is not entirely satisfactory since the tube must be put in place and then the sheet of water-repellent material or filter material positioned in its proper place. Alternatively, it might be possible to permanently or semi-permanently attach the water-repellent material or filter material to the tube; however, these tubes must be transported, stacked, and dragged across fields. In doing so, such a type of filtering material would become dislodged or removed.
Also, U.S. Pat. Nos. 2,763,991 and 2,052,020 show systems similar to that of the aforementioned Sixt patent, however, are objectionable for one reason or another.